R. Bettencourt et al., CELL-ADHESION PROPERTIES OF HEMOLIN, AN INSECT IMMUNE PROTEIN IN THE IG SUPERFAMILY, European journal of biochemistry, 250(3), 1997, pp. 630-637
The isolation of antibacterial peptides from the giant silkmoth Hyalop
hora cecropia has opened the area of animal antibiotics [Boman, H. G.
(1991) Cell 65, 205-207] and the study of insect immune genes has reve
aled striking similarities to many immune response gents in mammals [H
ultmark, D. (1994) Nature 267, 116-117], However, the molecules and me
chanisms behind primordial immune recognition are not understood. One
candidate for one such recognition molecule is hemolin, a 48-kDa immun
oglobulin-related protein first isolated from H. cecropia, where it is
up-regulated upon infection and secreted into the hemolymph. Hemolin
was shown to bind to bacteria and to hemocytes, giving rise to changes
in hemocyte adhesiveness and intracellular phosphorylation patterns [
Faye, I. Bi Kanost, hi. (1997) in Molecular mechanisms of immune respo
nses in insects (Brey, P. T. & Hultmark, D., eds) Chapman and Hall, Lo
ndon]. In the present publication, we give evidence for the presence o
f a 52-kDa membrane form of hemolin on hemocytes, based on flow-activa
ted cell sorting and membrane protein extractions. In addition we reve
al calcium-dependent hemophilic binding properties of hemolin, using h
emolin-coated microspheres. When biotinylated recombinant hemolin was
allowed to bind to hemocyte membranes, higher molecular-mass complexes
were formed. Furthermore, we used immunological methods and Northern-
blot analysis to demonstrate the presence of hemolin in embryos and re
tinal discs, suggesting that hemolin is expressed in several tissues a
t different developmental stages. These results show novel cell adhesi
on features of hemolin, corroborating its multifunctional character wi
th putative roles in cellular and humoral immunity and in development.